High rate packet data transmission system

ABSTRACT

A hybrid ARQ method for packet data transmission in a mobile communication system wherein previously transmitted packets are combined with retransmitted packets. The packets are segmented into a plurality of protocol data units (PDUs), and each PDU is assigned a sequence number for identification purposes. The sequence number is transmitted on a control channel which is separate from the data channel for transmitting the PDUs.

This is a divisional application of application Ser. No. 09/858,590,filed May 17, 2001 now U.S. Pat. No. 6,658,005.

FIELD OF THE INVENTION

The present invention relates to retransmission techniques in mobilecommunication systems, and, in particular, CDMA systems. Morespecifically, the present invention relates to a hybrid ARQ (automaticretransmission request) method for packet data transmission thatcombines previously transmitted packets with retransmitted packets. Witheach combining operation, redundancy is increased and the packet is morelikely to be received correctly even in hostile communicationenvironments. In more detail, the present invention relates to a hybridARQ method which is commonly referred to in the art as hybrid ARQ typeII, III, or incremental redundancy.

BACKGROUND OF THE INVENTION

A common technique for error detection of non-real time services isbased on Automatic Repeat request (ARQ) schemes which are combined withForward Error Correction (FEC), called hybrid ARQ. If an error isdetected by Cyclic Redundancy Check (CRC), the receiver requests thetransmitter to send additional bits of data.

From different existing schemes, the selective-repeat continuous ARQ ismost often used in mobile communications. This scheme in connection withFEC will be used for next generation mobile communication systems suchas UMTS (Universal Mobile Telecommunications System). A retransmissionunit of the RLC (Radio Link Control) layer is referred to as PDU(Protocol Data Unit).

In the art, three different types of ARQ are commonly defined asspecified below. Examples of corresponding prior art documents are:

Performance of punctured channel codes with ARQ for multimediatransmission in Rayleigh fading channels; Lou, H. and Cheung, A. S.;46th. IEEE Vehicle Technology Conference, 1996;

Analysis of a type II hybrid ARQ scheme with code combining, S. Kallel,IEEE Transactions on Communications, Vol. 38#8, August 1990; and

Throughput performance of Memory ARQ schemes, S. Kallel, R. Link, S.Bakhtiyari, IEEE Transactions on Vehicular Technology, Vol. 48#3, May1999.

Type I: The erroneous PDUs are discarded and a new copy of that PDU isretransmitted and decoded separately. There is no combining of earlierand later versions of that PDU.

Type II: The erroneous PDU that needs to be retransmitted is notdiscarded, but is combined with some incremental redundancy bitsprovided by the transmitter for subsequent decoding. Retransmitted PDUssometimes have higher coding rates and are combined at the receiver withthe stored values. That means that only little redundancy is added ineach retransmission.

Type III: Is the same as Type II with the only difference being thatevery retransmitted PDU is now self-decodable. This implies that the PDUis decodable without the need of forming a combination with previousPDUs. This is useful if some PDUs are so heavily damaged that almost noinformation is reusable.

Schemes of type II and III are obviously more intelligent and show someperformance gain because they have the ability to adjust the coding rateto changing radio environments and to reuse the redundancy of previouslytransmitted PDUs.

To support incremental redundancy, the sequence number (SN) of thetransmission unit has to be encoded separately. The stored data with theknown SN can then be combined with subsequent retransmissions.

In the prior art, the SN is encoded in the PDU header or in the timeslot header (e.g. EP-A-0938207) and transmitted together with the PDU.If the PDU is corrupted, it is likely that the header is also destroyed.Therefore, the coding has to be done with a lower coding rate to allowthe SN to be read even when the data is erroneous. As a result, a largecoding overhead exists to ensure reliable transmission of the sequencenumber. The coding for the SN therefore has to be different from thatused for the PDUs resulting into increased complexity. To ensure thatthe SN is correct, a CRC parity check could be applied, but reliable CRCover a few bits is not very efficient.

Besides the signalling overhead that is introduced by the prior artmethods, it is the implementation complexity that has prevented thistechnique from being used. A large amount of memory is required in thereceiver to store the erroneous packets for combining with theretransmissions. Since the SNs are not known before receiving theretransmission, it is not possible to start the combining process beforethe SNs have been decoded.

SUMMARY OF THE INVENTION

The object underlying the present invention is to provide a hybrid ARQmethod with less signalling overhead and low implementation complexity.The present invention overcomes the prior art problems since thesequence number is transmitted over a separate control channel. Thisallows for a reduction of the complexity of the receiver since thesequence number may be transmitted beforehand which allows a moreefficient decoding and combining of the PDUs which may follow at a latertime. Instead of storing the complete frame, decoding the SNs, combiningstored packets with now identified retransmitted packets and finallydecoding the packets, only the combining and decoding need to be done.Furthermore, delivery of the SNs on a separate channel makes theintroduction of this method into existing systems easy since the PDUformat and the complete mapping function in the medium access controlMAC layer can be left unchanged compared to a retransmission scheme notusing type II/III combining.

According to preferred embodiments, different channelization codes,different time slots and different frequencies are used for the controlchannel for transmitting the sequence numbers and the data channel fortransmitting the PDUs. This provides for gaining performance due to timeand frequency diversity and separate physical channels of the PDU andthe SN.

Preferably, the data channel for transmitting the PDUs is a channelshared by several users which allows more efficient use of the channelresources.

According to a preferred embodiment, the control channel fortransmitting the SNs is a low rate dedicated channel or a shared controlchannel in order to save channel resources.

According to a further advantageous embodiment, the quality of serviceQoS of the control channel is independent from the QoS of the datachannel for transmitting the PDUs by suitably controlling at least oneof the parameters comprising transmission power, coding rate andspreading factor. Consequently, transmission efficiency as well asreliable transmission of the sequence number is attained by separatelycontrolling the QoS for the SN and the PDU.

For higher data rates, it is advantageous to combine multiple sequencenumbers in a sequence number data unit SNDU in order to compress thesignalling and to increase CRC efficiency. Preferably, the SNDU ismultiplexed with other signalling data or user data to save channelresources. According to a further preferred embodiment, the SNDU is senttogether with an allocation message on the control channel for a shareduplink or downlink channel transmitting with a high data rate.

Depending on the used physical channel and the access technology, thereception of SNs and the PDUs are either not at all correlated withrespect to time or the correlation with respect to time is less.Although it is advantageous that the SNs of the SNDU arrive in the orderof the received PDUs, the high rate packet transmissions are less timeconstrained and allow for a time offset between the SN and thecorresponding PDU.

According to a further preferred embodiment, the SNDU is mapped to morethan one frame of the control channel which allows interleaving.

Further, it is preferred that correct reception of the SNDU is indicatedfrom the mobile station to the base station or vice versa as part of atransmission protocol.

If the sequence number is additionally included in the header of eachPDU, type III ARQ can be realized.

According to a further advantageous embodiment of the invention, themethod includes that a network control unit transmits a signalindicative of whether the hybrid ARQ method is to be employed or not.Alternatively, the signal can be transmitted from the mobile or basestation. As a variant, the base station and/or the mobile station canrecognize from the existence of a SNDU whether the hybrid ARQ method isto be employed or not.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail withreference to the accompanying figures, in which:

FIG. 1 shows a frame and slot structure of an DCH frame to which thepresent invention may be applied;

FIG. 2 shows a frame and slot structure of a DSCH frame to which thepresent invention may be applied.

FIG. 3 shows the time relation between the DCH frame and the associatedDSCH frame;

FIG. 4 shows the DCH frame data structure to be multiplexed on a 10 msframe; and

FIG. 5 shows a flow chart explaining the principles of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next generation mobile communication systems such as UMTS will providethe capabilities to transmit variable bit rate packet transmission.Traffic characteristics can be very bursty and need a fast channelallocation strategy. One example for a fast allocation scheme is the useof a shared channel, where a high rate packet channel is only allocatedto users actually having data to transmit. Thus, idle times of high ratededicated channels are minimized. In WO-A-00/02326, an example for ashared channel concept is given. The invention can advantageously beused with a high rate shared channel.

The build-up of a dedicated channel (DCH) as a permanent resource is notvery efficient to support packet traffic since the establishment of aDCH will take considerable time. Also, for CDMA communication systemsusing orthogonal codes, the available code resource is limited. The useof a downlink shared channel (DSCH) with fast resource allocation isseen as important for packet data because the data stream could havehigh peak rates but low activity cycles.

In the following, the invention shall be described by way of an exampleonly in connection with a downlink shared channel called DSCH. When ashared channel is used, the spreading codes for high rate code users areallocated frame by frame. There will be a signalling channel forallocation messages in parallel to the DSCH. This could be a sharedcontrol channel or a low rate associated channel. In the describedexample, a low rate dedicated channel DCH is allocated to each user tomaintain CDMA power control and to inform the mobile station when thereis data on the shared channel to decode. The DCH will be allocated ahigh spreading factor (SF) code (e.g. SF=256), but still represent aconsiderably large overhead.

FIG. 1 shows the frame and slot structure of the low rate DCH thatcontains pilot bits for coherent detection, TPC (Transmit Power Control)bits for power control, TFCI (Transport Format Control Indicator) bitsto indicate the transport format, and a data field. As indicated in FIG.1, a time slot contains 2560 chips, and 15 slots #0 to #14 form acomplete frame having a duration of 10 ms.

FIG. 2 shows the frame and slot structure of the DSCH which onlycontains data. The DSCH can transmit variable data rates whereasdifferent spreading factors (SF) are applied (k=0 . . . 6 relates toSF=256 . . . 4). The TFCI information transmitted on the DCH includesinformation about the spreading factor, the data rate and channelizationcode of the DSCH.

FIG. 3 shows the timing relation of the DSCH with one mobile station(with a low rate DCH) that might get data on the DSCH when there is datato transmit to the user. The timing of the DSCH is known since it issynchronous to other common channels. The high rate channel (DSCH) willonly be allocated on demand and is shared by several users. Accordingly,the data on the DSCH only needs to be decoded if there is data indicatedby the TFCI. The continuous DCH can, at the same time, be used totransport other data (e.g. circuit switched or other delay constraineddata) or signalling data. DSCH and DCH operate in an asynchronous manneras different DCH have different timing to each other, but the relativetiming is known to the mobile station and the data can be decodedcorrectly.

According to one aspect of the invention, the PDU sequence numbers willbe sent on a separate physical channel. In the preferred embodiment, theSNs are sent together with the allocation message to minimize thesignalling overhead needed for the packet transmission and theincremental redundancy scheme.

For CDMA communications systems, this implies that the channel where thesignalling data is mapped onto is spread with a different channelizationcode before the signal is modulated. This allows the QoS by this channelto be controlled separately from the channel where the PDUs are sent.For instance, the power level of the DCH can be increased to improve thereception of the SNs. In future mobile communication systems such asUMTS, it is also possible to transmit certain fields with differentpower. For instance, the power of the DCH data field can be differentfrom the TFCI, TPC or pilot power. The separation of control and userdata provides additional flexibility. Some systems are therefore alsousing separate protocol stacks for control and user plane of the ISO(International Standardization Organization) OSI (Open SystemInterconnection) protocol stack. A benefit of separating controlinformation from data is that the signalling can be combined with othersignalling thus providing more efficient transmission. To send the SNsover a different physical channel can also mean to send them in adifferent slot (e.g. TDMA) or on a different frequency (e.g. FDMA,OFDM).

In prior art systems, the sequence numbers are sent together with thePDU for unambiguous assignment and minimal delay. Typically, a strongblock code is used to encode single sequence numbers since only a coupleof bits have to be encoded. New packet data applications allow for somedelay that have not been acceptable for traditional circuit switchedapplications (e.g. speech). In the preferred embodiment of the presentinvention, the DCH frame that contains the allocation message (TFCI) forthe shared channel also delivers the SNs for the PDUs to be transmittedin the corresponding DSCH frame. With the combination of these twomethods, the signalling overhead of the shared channel concept andincremental redundancy is minimized by using the channel together. Alsoby this combination, the newly introduced delay is kept at a minimumbecause the allocation message is needed in any case if a high ratechannel is shared by multiple users. Simulations have shown that thedelay for packet data can even be reduced compared to a circuit switchedconnection since the ‘big pipe’ that is shared by multiple users is amore appropriate transmission scheme for applications where data doesnot arrive continuously. The time difference between the allocationmessage and the data packets has to be kept very small since, in amobile communication environment, the conditions can change quitefrequently.

The sequence numbers will be delivered as a higher layer signallingmessage in the data field of the DCH. Since the shared channels are onlyused for higher data rates, it is possible to combine them for reliableencoding and to use more suitable codes such as convolutional or turbocodes. In the following the packet with the SNs shall be called Sequencenumbers data unit—SNDU. FIG. 4 shows the most simple arrangement of SNs.Sequence numbers for all the packets in the next DSCH frame are arrangedin order and encoded by a 1/3 rate convolutional encoder. Beforeencoding, 8 bits for code termination are attached as a tail to the SNs.Other coding methods such as Turbo or BCH encoding could also be used.To ensure reliable reception, the data field is protected by a CRC codethat can have a variable size of 8, 12, 16 or 24 bits. The number ofPDUs in the DSCH frame and consequently the number of SN in the DCHframe that are transmitted can vary from 1 up to more than 100 dependingon the PDU size and the chosen data rate of the DSCH. After encoding,puncturing or repetition is applied to map the data onto the physicalchannel. Before slot segmentation, the data is interleaved over a frame(10 ms). Of course, it should be understood that this processing ofcoding and multiplexing is just given as a simplified example of anembodiment of the invention.

It is also possible that the SNDU is multiplexed together with othersignalling data with user data on the DCH. A major advantage of thescheme proposed is that it is possible to group multiple SNs together.ARQ protocols typically use a sliding window technique. That means thatexcept for the retransmissions, which are often sent with higherpriority, all packets are sent in order. Different arrangements of theSNs can be used to compress the actual information in the SNDU that issent over the air interface. For example, they do not have to be sent asa list in which each SN has around 6 to 12 bits. Instead, they could besent in series, e.g. 1−4 or 1+3, 7−12 or 7+5 instead of 1, 2, 3, 4, 7,8, 9, 10, 11, 12.

For a high rate shared channel that transmits several PDUs per frame, itwill be difficult to put the SNDU into a single frame while maintainingthe high spreading factor (e.g. 256, 512). A decrease of the spreadingfactor should be avoided to minimize the resources allocated in idletimes. It should therefore be possible to map the SNDU onto more thanone frame. The time offset between the DCH and the DSCH should take themaximum number of frames per SNDU into account. The interleaving sizecan also be increased to multiple frames or remains on a frame basis tomake the SNs available as soon as possible. SNs could also be sent onmultiple SNDUs to avoid large packet losses if a SNDU is corrupted.

An example shall be given in the following. The SNDU is mapped to twoframes, whereas interleaving is only done over 10 ms. The DCH/DSCHoffset is defined to a minimum of one frame. That means that the SNDUfirst frame is received before the corresponding DSCH frame, while thesecond SNDU frame is received simultaneously as the corresponding DSCHframe.

The retransmission window size and consequently the number of bitsrequired for the sequence number should also be kept as small aspossible to reduce the signalling overhead per PDU. A small window sizerequires that the round trip delay is as small as possible to speed upthe retransmissions and acknowledge process.

The SNs in the DCH data field easily identify whether incrementalredundancy is used or not before the PDUs are received. By this onceagain, receiver complexity is decreased since the reconfiguration of thereceiver can be done before the reception of the PDUs. Incrementalredundancy can easily be switched on/off by the proposed method, e.g.when the receiver runs out of memory.

The sequence numbers identify which PDUs shall be combined with eachother. For a correct operation, it is therefore essential that thesequence numbers are correct.

The CRC will provide an effective means to ensure that the SNDU isreceived correctly. Nevertheless, means have to be provided in theprotocol to resolve sequence number errors that are not detected. A highFEC encoding will ensure that the SNDU is received correctly even whensome or all PDUs are erroneous. There is a trade-off in reliability andcoding overhead. It might be more efficient to take regular failuresinto account instead of encoding data too reliably. A recognized problemis if the SNDU gets lost, all the PDUs of the corresponding frame aresent on the DSCH even though they can not be identified.

A variant of the invention is that the mobile station will send anindicator on the uplink DCH to the base station after the correctreception of a SNDU. Only when this indicator is received by the basestation, the PDUs are sent on the DSCH. If the indicator is notreceived, the PDUs will not be sent and interference will be minimized.

For hybrid ARQ Type III, each PDU is self-decodable, meaning that theycan theoretically be decoded without any combining with previous PDUs.Enough information is provided in each PDU to decode it withoutcombining. For such schemes, a different approach has been foundbeneficial. The SNDU is also delivered on a separate channel but is notvery strongly encoded. At the same time, the sequence number isadditionally transmitted as part of the header in the PDU, as in theusual operation. The header is included in the RLC layer. If the SNDU isreceived correctly, the reception can be improved by PDU combining. Ifthe SNDU is lost, the PDUs can still be decoded without combining (ifreception quality allows) because the sequence number in the PDU headeridentifies the PDU for the RLC layer. By this, the coding overhead forSNDUs is decreased and the protocol can still work efficiently if theSNDU is lost. There are other advantages of this approach since it ispossible to separate the RLC retransmission protocol completely from there-combining process in the physical layer. If it is intended not to useSNDU transmission, the RLC layer protocol is exactly the same as withoutHybrid ARQ Type III. This allows the combining operation to be switchedoff without any impact on RLC protocol, the PDU structure or the DSCHtransmission in general. The drawback is that there is redundantinformation in the PDU header sent in cases where the SNDU is receivedcorrectly.

In the following, a preferred embodiment of the method of the inventionis explained with reference to FIG. 5.

When a mobile station sets up a packet data session in step 100 (e.g.Internet access), the Base Station can decide, depending on theapplication, to use the DSCH for that user. A dedicated channel isestablished in up- and downlink. A transport format control indicator(TFCI) which defines the possible data rates on the DSCH is allocated bythe base station and signalled to the mobile station.

If there are packets arriving at the base station, the data will besegmented in step 200 into PDUs. Now, the SNs are assigned to the PDUs(step 210) before they are stored according to step 220 for possibleretransmission. Once enough PDUs are accumulated to be sent on the DSCH,the base station will schedule a frame on the DSCH for this user (step230). The sequence numbers will be multiplexed, encoded according toFIG. 4 and mapped on the control channel as shown in step 240.Subsequently, the base station transmits the control channel includingthe TFCI on the DCH to the mobile station. In step 250, the PDUs aremultiplexed, encoded and mapped on the data channel which is sent on theDSCH. With the specified timing (see FIG. 3), the mobile stationreceives the DCH and hence will be informed via TFCI (step 230) on theDCH (signal is spread with spreading code x) about the data to bedecoded on the DSCH (signal is spread with spreading code y) and itstransport format. In the same DCH frame (or the following frames ifmapped to several frames), the sequence numbers will be signalled to,and decoded by, the mobile station (step 260). As a result, the mobilestation knows exactly the beginning of the DSCH frame and will receiveand decode the PDUs on the DSCH (step 270) sent in step 250.

The storage of erroneous PDUs (step 280) and the combining withretransmissions (step 270) will take place according to an implementedalgorithm that is outside of the scope of this description. Allcorrectly decoded packets are transmitted to the higher layers.Unsuccessfully decoded packets will be stored for recombining withretransmissions. Acknowledge (ACK) and Not-Acknowledge (NACK) messages(step 290) will be sent to the transmitter according to the implementedRLC protocol.

The mobile station will wait for new packets to be transmitted as longas the session is ongoing (return to step 220) and the user is likely touse the DSCH.

For future systems, it will be common that there are multiple logicalchannels mapped on the physical channel. A logical channel might consistof control data or user data and can belong to different applications orprotocol entities. The multiplexing of the transport channel does notnecessarily take place in the physical layer but is likely to beaccomplished by the Medium Access Control (MAC) Layer. For incrementalredundancy, this higher layer multiplexing is problematic because atransport block that is passed to the physical layer for transmissioncan consist of data from different logical channels. After decoding, oneof the blocks might be correctly received while the other is erroneous.A retransmission has to be done based on the originally sent data. Theexact data block including the correctly received data part would haveto be retransmitted to make the recombining process work. Some of thelogical channels might not even use ARQ if they have a low QoSrequirement.

Another characteristic of the present invention is to switch off the MACmultiplexing to make incremental redundancy more efficient. This can bedone in connection with the decision to use incremental redundancy ornot. This will ensure that if incremental redundancy is used, differentlogical channels are passed as separate transport channels to thephysical layer. In addition to the transport blocks for each transportchannel, further information is given to the physical layer ifincremental redundancy shall be used or not. Incremental redundancy isonly possible for logical channels that apply ARQ (that are inacknowledged mode).

The particular transport channel which will use incremental redundancy,in the downlink, also will depend on the capabilities of the mobileterminal. The main limitation in the terminal will be lack of memory tostore the soft-decision values. If the mobile terminal can not supportincremental redundancy for all transport channels, incrementalredundancy can be switched off for some transport channels.

1. A hybrid ARQ method for packet data transmission in a mobilecommunication system, said method comprising: transmitting the packetdata on a data channel in a form of a plurality of protocol data units;and assigning an indicator to each protocol data unit; wherein theindicator is transmitted on a control channel with an allocation messagewhich includes information about the channelization code of the datachannel.
 2. A hybrid ARQ method according to claim 1, wherein theindicator is a sequence number.
 3. A hybrid ARQ method according toclaim 1, wherein the indicator indicates whether to combine the protocoldata unit with a protocol data unit transmitted previously.
 4. A hybridARQ method according to claim 1, further comprising storing at least oneof the plurality of protocol data units for subsequent retransmission.5. A hybrid ARQ method according to claim 1, further comprisingreceiving a request for retransmission of at least one of the pluralityof protocol data units.
 6. A hybrid ARQ method according to claim 1,further comprising: storing at least one of the plurality of protocoldata units for subsequent retransmission; receiving a retransmissionrequest for the at least one stored protocol data unit; andretransmitting the at least one stored protocol data unit.
 7. A hybridARQ transmission apparatus comprising: a transmission section operableto transmit packet data on a data channel in a form of a plurality ofprotocol data units, and to assign an indicator to each protocol dataunit; wherein the indicator is transmitted on a control channel with anallocation message which includes information about the channelizationcode of the data channel.
 8. A hybrid ARQ transmission apparatusaccording to claim 7, wherein the indicator is a sequence number.
 9. Abase station apparatus equipped with said transmission apparatusaccording to claim
 7. 10. A hybrid ARQ reception apparatus comprising areceiving section operable to receive the data transmitted by saidtransmission apparatus according to claim
 7. 11. A transmission systemcomprising: a transmission apparatus, said transmission apparatuscomprising a transmission section operable to transmit packet data on adata channel in a form of a plurality of protocol data units, and toassign an indicator to each protocol data unit, wherein the indicator istransmitted on a control channel with an allocation message whichincludes information about the channelization code of the data channel;and a reception apparatus operable to receive the protocol data unit andthe indicator transmitted by said transmission apparatus.
 12. A hybridARQ reception apparatus comprising: a receiving section operable toreceive packet data on a data channel in a form of a plurality ofprotocol data units, and to receive a plurality of indicators on acontrol channel, each of the plurality of indicators being associatedwith one of the plurality of protocol data units; and a decoding sectionoperable to decode the received protocol data units; wherein saidreceiving section is further operable to receive an allocation messagethat is transmitted with at least one of the indicators on the controlchannel; and wherein the allocation message includes information aboutthe channelization code of the data channel.
 13. A hybrid ARQ receptionapparatus according to claim 12, further comprising a combining sectionoperable to combine a retransmitted protocol data unit with a previouslyreceived protocol data unit based on the indicators.
 14. A hybrid ARQreception apparatus according to claim 12, further comprising atransmitting section operable to transmit a request for retransmissionof a protocol data unit if the received protocol data unit is notsuccessfully decoded.
 15. A hybrid ARQ reception apparatus according toclaim 12, further comprising: a transmitting section operable totransmit a request for retransmission of a protocol data unit if thereceived protocol data unit is not successfully decoded; and a combiningsection operable to combine a retransmitted protocol data unit that wasreceived according to the request with a previously received protocoldata unit based on the indicators.
 16. A hybrid ARQ reception apparatusaccording to claim 12, wherein the indicators are sequence numbers. 17.A mobile station equipped with said hybrid ARQ reception apparatusaccording to claim
 12. 18. A method for receiving data packets by amobile station, said method comprising: initiating a data packet sessionthat establishes a data channel and a control channel; receiving packetdata on the data channel in a form of a plurality of protocol dataunits; receiving, on the control channel, a plurality of indicators,each of the plurality of indicators being associated with one of theplurality of protocol data units; receiving an allocation messagetransmitted with at least one of the indicators, wherein the allocationmessage includes information about the channelization code of the datachannel; and decoding the received protocol data units.
 19. A methodaccording to claim 18, further comprising transmitting a resubmissionrequest based on a determination that one of the received protocol dataunits was not successfully decoded.
 20. A method according to claim 19,further comprising: receiving a retransmitted protocol data unit basedon the resubmission request; and combining the retransmitted protocoldata unit with the non-successfully decoded protocol data unit based onthe indicators.